A Groundbreaking Discovery on Mars
Among several recent findings, the rover has found rocks made of pure sulfur — a first on the Red Planet. Scientists were stunned on May 30 when a rock that NASA’s Curiosity Mars rover drove over cracked open to reveal something never seen before: yellow sulfur crystals.
Exploring Sulfur-Rich Regions
Since October 2023, the rover has been exploring a region of Mars rich with sulfates, a type of salt that contains sulfur and forms as water evaporates. While previous detections have been of sulfur-based minerals (a mix of sulfur and other materials), the rock Curiosity recently cracked open is made of elemental, or pure, sulfur. The relationship, if any, between the elemental sulfur and other sulfur-based minerals in the area remains unclear.
Interestingly, while sulfur is often associated with the odor of rotten eggs due to hydrogen sulfide gas, elemental sulfur is odorless. It forms under specific conditions not typically linked to the history of this location. Curiosity found a significant amount of it — an entire field of bright rocks similar to the one it crushed.
Curiosity’s Mission in Gediz Vallis Channel
“Finding a field of stones made of pure sulfur is like finding an oasis in the desert,” said Ashwin Vasavada, Curiosity’s project scientist at NASA’s Jet Propulsion Laboratory. “It shouldn’t be there, so now we have to explain it. Discovering strange and unexpected things is what makes planetary exploration so exciting.”
This discovery is one of several made by Curiosity within the Gediz Vallis channel, a groove winding down part of the 3-mile-tall Mount Sharp. The rover has been ascending this mountain since 2014. Each layer represents a different period in Martian history, and Curiosity’s mission is to study whether ancient terrain could have supported microbial life.
Scientists believe Gediz Vallis channel was carved by flows of liquid water and debris, leaving a ridge of boulders and sediment extending 2 miles down the mountainside. Understanding this landscape’s changes over billions of years is a key goal, and recent clues have provided valuable insights.
Analyzing the Martian Terrain
Since arriving at the channel, scientists have studied whether ancient floodwaters or landslides created the large mounds of debris. The latest clues suggest both played a role: some piles were left by violent flows of water and debris, while others resulted from local landslides.
The evidence is based on rocks found in the debris mounds. Stones carried by water flows become rounded, like river rocks, while angular rocks found in some mounds may have been deposited by dry avalanches. Water also soaked into the settled material, causing chemical reactions that bleached white “halo” shapes into some rocks. Erosion from wind and sand has revealed these shapes over time.
“This was not a quiet period on Mars,” said Becky Williams, a scientist with the Planetary Science Institute and deputy principal investigator of Curiosity’s Mast Camera. “There was an exciting amount of activity here, including multiple flows down the channel, energetic floods, and boulder-rich flows.”
Curiosity’s team has been eager to take rock samples from the channel to learn more. On June 18, they found their opportunity. While the sulfur rocks were too small and brittle for sampling, a large rock nicknamed “Mammoth Lakes” was spotted nearby. Rover engineers found a safe drilling spot on the loose, sloping surface.
After drilling its 41st hole, Curiosity trickled the powderized rock into its instruments for further analysis. Scientists aim to determine the rock’s materials. Curiosity has since moved on, ready to uncover more surprises within the channel.
An earlier version of this article was published in July 2024.
